The invention relates to incandescent lamps and particularly to equipment which utilize such lamps to provide light for the production of motion pictures. Such equipment will hereinafter be referred to as "movie lights."
A recent development in the motion picture field is the "instant movie" system designed by the Polaroid Corporation, Cambridge, Mass. This system includes an automatic-exposure movie camera in which a film-containing cassette is used. Exposure of the film occurs within the cassette which is inserted within a special projector, or "player" and the film projected on the player's screen. Processing of the film requires only about ninety seconds.
The present invention is especially adapted for utilization with the above movie system, in addition to other systems requiring similar levels of illumination. As will be described, the present invention is electrically operated and fully capable of being mounted on a movie camera such as the above. Understandably, the function of the invention is to substantially uniformly illuminate a subject field located at a prescribed distance from the camera during periods of use in which normally satisfactory illumination is not otherwise available. By uniformly illuminated is meant a corner-to-center illumination ratio within the range of about 0.32 to about 0.45 for a rectangular subject field located at a distance of approximately fifteen feet from the movie camera. That is, the center of the subject field at this distance requires a level of illumination of about three times the level needed for the corners of the field. A typical field is about fifty-eight inches (vertical) by seventy-eight inches (horizontal). A desired luminous intensity at the center of the field is within the range of about 14,000 to 17,000 candelas while that of the respective corners of the field is within the range of about 5,000 to 7,000 candelas.
Most known systems capable of providing the above illumination are relatively expensive to both operate and purchase as well as very awkward to operate when used in conjunction with movie cameras.
In the system of Ser. No. 939,928, the movie light contains two low voltage incandescent lamp units, each having a single, planar filament therein. Each unit has an operating voltage of 50 to 65 volts. In the high voltage movie light system defined by the present invention, each of the lamp units has an operating voltage within the range of from about 100 to about 130 volts. Accordingly, the movie light has a total operating voltage of about 200 to 260 volts when the lamp units are joined in series. This makes the movie light ideally suited for high-voltage environments such as Europe. The increased operating voltage is possible as a result of providing each lamp with a dual filament structure secured within the lamp in a more positive manner than the single filaments employed in the lamps of Ser. No. 939,928. The intensity distribution produced on a subject field by each unit in the movie light is bimodal which assures a relatively uniform illumination of the field. It is also possible in the present invention to employ a single unit as the movie light, thus making the system suited for use in normal line voltage, e.g. 100 to 120 volts, environments such as this country.
It is believed, therefore, that a high voltage movie lighting system which is capable of providing the above-desired levels of illumination would constitute an advancement in the art. It is further believed that a lamp unit capable of being used as part of such a system or singularly as a movie light would also constitute an advancement in the art.